The present invention relates generally to the primary structure of a member of the serpin superfamily of proteinase inhibitors from the insect Manduca sexta. More specifically, the present invention relates to a cDNA clone isolated from a fat body cDNA library from a lepidopteran insect, the tobacco hornworm M. sexta, and the deduced amino acid sequence of the serpin.
The serpins are a superfamily of serine proteinase inhibitors. Human plasma contains serpins which are similar in amino acid sequence and mechanism of inhibition, but differ in their specificity toward proteolytic enzymes. The serpin superfamily includes proteins of about M.sub.r =50,000-100,000, which function in regulation of blood clotting (antithrombin-III, heparin cofactor-II, antiplasmin, protein C inhibitor), complement activation (C1 inhibitor), and proteinases released from neutrophils (.alpha.,-antitrypsin,.alpha.,-antichymotrypsin). The serpin superfamily also includes endothelial plasminogen activator inhibitor, glia-derived nexin, mouse contrapsin, ovalbumin, angiotensinogen, barley endosperm protein Z, and cowpox virus 38-kDa protein. Comparisons of the amino acid sequences of these individual serphins reveal an sequence identity of about 20-30%, with the greatest sequence conservation appearing at the COOH-terminal half of the proteins.
In contrast, much less is known about proteinase inhibitors from invertebrates. Most of the proteinase inhibitors isolated from invertebrates have been in the low M.sub.r range of about 5,000-15,000. A M.sub.r =155,000 proteinase inhibitor has been isolated from crayfish plasma and an .alpha..sub.2 -macroglobulin-like proteinase inhibitor has been isolated from hemolymph of the American Lobster.
The only proteinase inhibitors isolated from invertebrates which are similar in size and characteristics to the serpins are a trypsin inhibitor (M.sub.r =42,000) and a chymotrypsin inhibitor (M.sub.r =43,000) which have been isolated from the hemolymph of the silkworm Bombyx mori. While some bioreactive similarities with the serpins exist, sequencing of the first 18 NH.sub.2 -terminal amino acids of these two silkworm proteinase inhibitors have revealed no similarity to the human serpins. The complete sequence data, which would show whether these silkworm proteins are evolutionarily related to the serpins, is not yet available.